1. Field of the Invention
The present invention relates to a voltage generating circuit used in a semiconductor storage, an SoC or the like.
2. Description of the Related Art
With advancement of miniaturization, low voltage operation, and high integration of semiconductor devices, semiconductor chips for a semiconductor storage, a system on a chip (SoC) and the like have become equipped with a built-in voltage generating circuit for generating a different voltage from an external supply voltage. There are two types of circuits as the voltage generating circuit, that is, a voltage step-down circuit that steps down an external supply voltage and a voltage step-up circuit that steps up an external supply voltage. Furthermore, two types of circuits are used as the voltage step-down circuit: one is a voltage generating circuit (such as a series regulator) that is used, for example, in a standby mode in which an electric current does not flow much; and the other is a voltage generating circuit that includes a source follower type of output transistor, and is used, for example, in an active mode in which a current flows. In general, in the voltage generating circuit of the source follower type, a mirror transistor is provided in a preceding stage of an output transistor. The mirror transistor is of the same type as the output transistor and is diode-connected (gate-drain connection) (Refer to Japanese Patent Application Publication No. 2003-178584, page 8, FIG. 10, (Patent Document 1), for example).
When a source follower type of voltage generating circuit described in Patent Document 1 and the like changes from the standby state to the active state, or from the active state to the standby state, a gate voltage of the source follower type of step-down transistor fluctuates, thereby causing a fluctuation of an internal supply voltage that has been stepped down and outputted. For this reason, a stabilizing capacitor having a large capacity is generally provided on the output side, as a normal measure against gate voltage fluctuations in the source follower type of step-down transistor. Mounting such a large-capacity stabilizing capacitor in a large-scale integrated circuit (IC or LSI) including a voltage generation circuit causes a problem of increase of the chip area.